1. Field of the Invention
The present invention relates to an electrophotographic copier, and more particularly to an electrophotographic copier employing a photosensitive (photoconductive) belt.
2. Description of the Prior Art
Electrophotographic copiers according to the Carlson process operate in complex processes. The construction and operation of such a copier will be briefly described below.
The surface of a photosensitive body is uniformly charged by a charging corotron, and a light image reflected from an original document which is illuminated with light is focused through a lens system onto the photosensitive body, thereby forming an electrostatic latent image. Toner is applied by a development unit to the electrostatic latent image, which is turned into a visible toner image. The toner image is then transferred electrostatically to a transfer sheet by a transfer corotron. The transfer sheet carrying the toner image is discharged by a peeling AC corotron, and is peeled off the photosensitive body and delivered to a fixing unit. Residual toner which has not been transferred to the transfer sheet is scraped off the photosensitive body by a cleaning blade. Thereafter, the photosensitive body is discharged by a discharge AC corotron. Then, the electrophotographic copier enters a charging process again.
With the above arrangement, the electrophotographic copier requires several corotrons for charging, transferring, peeling, and discharging, and also a toner collector box for storing toner scraped off by the cleaning blade. Therefore, the copier is complex in construction. Where the photosensitive body comprises a drum, the drum has a large diameter and the body of the copier is necessarily large in size.
In general, toner tends to be scattered from the development unit into the copier body. The conventional copier is disadvantageous in that the toner from the development unit smears the transfer sheet, the corotrons, and even the lens.
Since the amount of toner which is not transferred to the transfer sheet is large, various proposals have been made to reuse such toner for thereby lowering the operating cost. However, any device for delivering toner from the toner collector box is liable to be complicated in structure.
The photosensitive bodies used include a belt and a drum. The photosensitive belt is more difficult to detect in its angularly displaced position than the photosensitive drum. One solution proposed heretofore is to provide prongs on the outer periphery of a roller which drives the photosensitive belt, the prongs being fitted in holes in the photosensitive belt to drive the belt at the same speed as that of the roller. The angular displacement of the photosensitive belt can be determined by detecting the rotational position of the roller. Since the photosensitive belt is forcibly driven by the prongs, the holes in the photosensitive belt in which the prongs fit have to be sufficiently reinforced. Another solution is to put a marking on a transverse edge of the photosensitive belt and to read the marking with a sensor. This arrangement has a drawback in that deposits of toner on the photosensitive belt are likely to cause the sensor to produce a readout error.